1. Field of Invention
This invention relates generally to work transfer systems and more particularly to an automated system in which a robot running on a rail along the front side of a work bench having an assembly of processing tanks at various positions thereon, acts to convey a work basket in a programmed sequence to each of the tanks, the robot acting to properly orient the work basket with respect to each tank before the basket is immersed therein.
2. Prior Art
By using diffusion techniques it is now possible to fabricate transistors and diodes as well as resistors and capacitors within a single wafer of silicon to create integrated circuits. The manufacture of microelectronic devices entails sequences of photolithography, etching and critical cleaning processes. For the most part, these have heretofore been carried out manually at wet chemistry work benches. In the usual manufacturing procedure, batches of substrates or silicon wafers are carried in "boats" and transferred from one chemical tank to another by a human operator who adjusts the conditions prevailing in each tank and also determines the periods during which the boat dwells in the respective tanks for treatment therein.
While automated transfer operations are now commonplace in many industrial processes including electroplating, there are a number of practical factors which have heretofore militated against the introduction of automation in the processing of microelectronic devices. A major factor is that the value of the microelectronic devices is high relative to the cost of labor involved in making these parts. Thus the introduction of automated work transfer mechanisms to reduce labor costs may not be economically justified, particularly when one takes into account the capital investment dictated by automated equipment.
But other factors now come into play which have little to do with the cost effectiveness of replacing manual operations with automated work transfer mechanisms. As microelectronic devices become increasingly complex and sophisticated, the associated wet chemistry procedures are rendered even more critical. As a consequence, the variables and human errors incidental to manual operation can no longer be tolerated, for repeatability and consistency are now the primary desiderata. Hence, these considerations may override the cost effectiveness factor.
Though efforts have been made to automate work transfer operations in wet chemistry processing of microelectronic devices, they have had limited success, largely because of certain environmental problems. Many of the chemical processing tanks used in micro device and wafer processing act to discharge corrosive vapors into the work area in the region immediately above the process tanks. Since the hoist is for the most part required to operate within this corrosive environment, the freely moving, unanchored hoist type of work transfer mechanism such as are employed in the printed circuit board plating industry have not been readily adaptable to this very different and specialized type of use.
Instead, fixed-sequence transfer mechanisms have been quite widely used. These enjoy the advantage of lesser vulnerability to the corrosive environment by reason of the reduced complexity of that part of the mechanism which is exposed to the environment. However, they suffer from the limitation that work transfer takes place only between two immediately adjacent tanks. In general, a single, common processing cycle time must be used.
As a consequence, the corrosive nature of the environment associated with many of the wet chemistry processes in microelectronic device and wafer fabrication has hitherto tended to discourage the use of an unanchored, horizontally-free tracking hoist or robot in this industry.
In my above-identified copending application whose entire disclosure is incorporated herein by reference, a work transfer system is disclosed in which a robot is provided having a hand adapted to grasp the handle of the basket and to manipulate the basket in accordance with programmed instructions, whereby the basket may be made to carry work in any desired sequence along a row of processing tanks disposed on a work bench. In that system, the entire transfer mechanism, but for the robot and hand its supporting arms, lies outside of the corrosive environment and need not, therefore, be protected against corrosion.
In my prior transfer system, a rail is disposed adjacent the front side of the work bench in parallel relation to the uniform row of tanks thereon. Riding on this rail is a robot having a pair of vertical shafts extending upwardly therefrom, the shafts being supported on an elevator platform disposed within this robot. A pair of arms are cantilevered from the upper ends of these shafts, the arms extending over the work bench. The extremities of these arms are pivotally connected to a cross piece from whose center depends a rod terminating in a hand adapted to engage the handle of the work basket.
In operation, when the robot is instructed to carry the work basket to a selected tank, the robot is caused to travel on the rail to a position at which the hand and the basket borne thereby are in general alignment with this tank. At this point, the shafts are rotated to angle the cross piece and thereby turn the rod carrying the hand to orient the work basket so that it is properly oriented with respect to the selected tank therebelow. And by then operating the robot elevator, one may lower the work basket into the tank for processing, and later lift the basket from the tank, so that the basket can then be transferred to another processing tank on the work bench.
There are, however, some work bench tank set-ups for which my prior system is unsuited. Thus, where instead of a single uniform row of tanks as in my copending application, there is more than one row of such tanks on the bench; or where instead of a uniform row, the tanks are randomly dispersed or are not oriented in the same direction, the complex motions then required of the work transfer system to properly orient the basket with respect to a given tank cannot be executed.
In my prior system, the length of the cantilever arms cannot be automatically adjusted to effect a fore and aft movement of the work basket toward or away from either long side of the work bench. Thus if one tank is close to the robot which runs on a rail parallel to the front side of the bench and another tank is more distant from the robot, my prior system is incapable of transferring the basket from the first to the second tank.